1. Field
The disclosure relates to the field of tire manufacture and more particularly to the tire building operations during which rubber products comprising reinforcing threads are joined or butted together.
2. Description of Related Art
These products are formed of a complex preassembly of continuous strips of rubber superposed on one another with determined overlap geometries. These preassemblies are performed with a view to reducing the final time taken to build the green tire by reducing the number of elementary products that have to be applied by winding to the tire-building drum.
In a known way, continuous strips of profiled elements intended to form the side wall and the bead region of a tire, for example, are preassembled.
Other preassemblies may comprise a greater number of elementary profiled elements such as, for example, an edging rubber reinforcing rubber and, in the specific case of the invention, a reinforcing ply comprising textile or metal reinforcing threads coated in rubber and making a given angle with the longitudinal direction of the ply. As a general rule, the reinforcing ply is only partially superposed on the rubber profiled elements.
These preassembled products are intended, for example, to form the bottom zone of a heavy vehicle tire, for which particular precautions are taken in order to protect this zone from mechanical and thermal attack.
During final build, a portion of given length is taken from the preassembled continuous strip formed of several elementary profiled elements or reinforcers and this portion is applied by winding around the tire-building drum of generally cylindrical shape.
It is therefore appropriate for the length of the portion of preassembled products to correspond very precisely to the circumference of the tire-building drum at the axial position assigned to it.
However, the cutting of these complex assemblies requires special attention.
Firstly, it is actually found that when the reinforcing ply is being cut, something which has to be done by running a cutting means between two threads, at the angle formed by these threads with the longitudinal direction of the strip, that the line along which the cutting means passing between two threads runs does not correspond to the theoretical cutting line determined after measuring the desired theoretical length of the portion of preassembled products that is to be applied to the tire-building means.
Secondly, it is often desirable to cut, using a separate cutting means, and at a different angle, the part of the rubber profiled elements that is not superposed on the reinforcing ply, in order for example to avoid laying and connecting front and rear edges that make a small angle with respect to the longitudinal direction.
There is therefore the issue of precisely determining the point at which two cutting lines meet so as to obtain a controlled geometry of the front and rear edges of the portion of preassembled complex products with a view to carrying out the operation of butting together these two edges which has to be performed on the tire-building drum.
This difficulty is amplified by the geometric variations in the products preassembled within the permitted manufacturing tolerances, it being possible for the said variations to affect both the angles of the threads and the widths of the reinforcing plies or of the rubber profiled elements.